Using the first commercially available 100 Gbps Ethernet technology with a link of varying length, we have evaluated the performance of the Lustre file system and its networking layer under different latency scenarios. The results led us to a better understanding of the impact that the network latency has on Lustre's performance. In particular spanning Lustre's networking layer, striped small I/O, and the parallel creation of files inside a common directory. The main contribution of this work is the derivation of useful rules of thumbs to help users and system administrators predict the variation in Lustre's performance produced as a result of changes in the latency of the I/O network.